The present invention relates to a mobile radio communication device such as a portable telephone which performs communication with a base station using a downlink frequency and an uplink frequency which are assigned to the mobile radio communication device by the base station, and in particular, to a mobile radio communication device which is provided with functions for detecting occurrence of interference to the downlink frequency and/or the uplink frequency and informing the base station of the occurrence of the interference.
Post-detection selective space diversity systems provided with two reception systems are generally employed for ensuring stable radio wave reception and communication even when electric field intensity is decreased due to fading which is characteristic of mobile communication, in which a post-detection reception signal having higher post-detection field intensity is selected from two reception signals which have been received by the two reception systems.
FIG. 1 is a block diagram showing composition of a conventional mobile radio communication device (a mobile terminal 5) which employs the post-detection selective space diversity system. The mobile terminal 5 is provided with two reception systems RA and RB each of which is composed of a double superheterodyne system in which demodulation of the reception signal is executed after two steps of frequency conversions. Along with the reception systems RA and RB, the mobile terminal 5 is provided with a transmission system TA. A first oscillator 35 and a second oscillator 36 are provided in order to generate a first local oscillation signal and a second local oscillation signal to be used for the first frequency conversion and the second frequency conversion (double superheterodyne) which are performed in each of the reception systems RA and RB. The first oscillator 35 is also used by the transmission system TA for converting the frequency of a modulated signal for being transmitted into a transmission frequency.
The reception system RA of the mobile terminal 5 is provided with an antenna ANT1 for receiving a radio wave having a downlink frequency frx (a frequency transmitted by an unshown base station to the mobile terminal 5). The reception system RB is provided with an antenna ANT2 for receiving a radio wave having the downlink frequency frx and transmitting a radio wave having an uplink frequency ftx (a frequency transmitted by the mobile terminal 5 to an unshown base station).
The reception system RB is provided with an antenna switch 30 for switching the function of the antenna ANT2 between reception and transmission. Hereafter, with respect to components which are common to both the reception systems RA and RB, explanation will be given on the reception system RA only, and reference numbers in round brackets ( ) represent components of the reception system RB which are equivalent to components of the reception system RA. In the example of FIG. 1, the reception system RA (RB) is provided with a band pass filter (BPF) 10 (20) for limiting the bandwidth of the reception signal (i.e. for rejecting unnecessary signals) supplied from the antenna ANT1, and a high frequency amplifier 11 (21) for amplifying the reception signal.
Further, the reception system RA (RB) of the mobile terminal 5 is provided with a BPF 12 (22) for further limiting the bandwidth of the reception signal supplied from the high frequency amplifier 11 (21), a first mixer 13 (23) for converting the reception signal into a first intermediate frequency signal (first IF signal) utilizing the first local oscillation signal supplied from the first oscillator 35, a BPF 14 (24) for limiting the bandwidth of the first IF signal supplied from the first mixer 13 (23), and a first intermediate frequency amplifier 15 (25) for amplifying the first IF signal supplied from the BPF 14 (24).
Further, the reception system RA (RB) is provided with a second mixer 16 (26) for converting the first IF signal into a second intermediate frequency signal (second IF signal) utilizing the second local oscillation signal supplied from the second oscillator 36, a BPF 17 (27) for limiting the bandwidth of the second IF signal supplied from the second mixer 16 (26), and a second intermediate frequency amplifier 18 (28) for amplifying the second IF signal supplied from the BPF 17 (27). After the second intermediate frequency amplifier 18 (28), the reception system RA (RB) is provided with an RSSI section 19 (29) for outputting an RSSI (Received Signal Strength Indicator) signal whose signal level varies according to the field intensity of the reception signal (the second IF signal), and a demodulator 19a (29a) for demodulating the second IF signal and thereby outputting a demodulated signal such as a baseband signal.
The transmission system TA of the mobile terminal 5 is provided with a modulator 31 for modulating the baseband signal utilizing the first local oscillation signal supplied from the first oscillator 35, a driver amplifier 32 as a preliminary amplifier for obtaining gain, and a power amplifier 31 for amplifying the modulated signal and supplying the amplified transmission signal to the antenna ANT1 via the antenna switch 30.
In the following, the operation of the conventional mobile radio communication device will be described. Incidentally, explanation of the operation of the transmission system TA is omitted for brevity.
In the reception system RA, a reception signal with the downlink frequency frx which has been received by the antenna ANT1 and whose bandwidth has been limited by the BPF 10 is supplied to the high frequency amplifier 11. Meanwhile, in the reception system RB, a reception signal with the downlink frequency frx which has been received by the antenna ANT2 at the same time is supplied to the antenna switch 30. When signal reception is performed, the antenna switch 30 is controlled by an unshown CPU etc. so as to connect the movable terminal c to the fixed terminal b, and thus the reception signal is supplied from the antenna switch 30 to the high frequency amplifier 21 via the bandwidth limiting BPF 20.
Thereafter, the reception systems RA and RB operate in the same way, therefore, only the operation of the reception system RA will be described in the following. Incidentally, reference numbers in round brackets ( ) represent components of the reception system RB. The reception signal outputted by the high frequency amplifier 11 (21) is supplied to the first mixer 13 (23) via the bandwidth limiting BPF 12 (22). The first mixer 13 (23) is also supplied with the first local oscillation signal from the first oscillator 35, and the reception signal is frequency converted by the first mixer 13 (23) into the first IF (intermediate frequency) signal having the first intermediate frequency which is lower than the downlink frequency frx.
The first IF signal is supplied to the second mixer 16 (26) via the BPF 14 (24) and the first intermediate frequency amplifier 15 (25). The second mixer 16 (26) is also supplied with the second local oscillation signal from the second oscillator 36, and the first IF signal is frequency converted by the second mixer 16 (26) into the second IF (intermediate frequency) signal whose frequency is lower than the first IF signal. The second IF signal outputted by the second mixer 16 (26) is supplied to the RSSI section 19 (29) and the demodulator 19a (29a).
The demodulator 19a (29a) demodulates the second IF signal and thereby outputs a demodulated signal such as a baseband signal to the unshown CPU etc. Meanwhile, the RSSI section 19 (29) outputs the RSSI (Received Signal Strength Indicator) signal having a signal level corresponding to the field intensity of the reception signal (the second IF signal) into the CPU via an unshown A/D converter. Then, the CPU selects one demodulated signal having larger intensity from the two demodulated signals supplied from the reception systems RA and RB by comparing the RSSI signals, and acquires the demodulated signal having larger intensity. Signal reception according to the post-detection selective space diversity system is performed by the conventional mobile radio communication device as described above.
However, in the above conventional mobile radio communication device of FIG. 1, when interference occurred between the reception signal having the downlink frequency frx and other radio waves (interfering signals), or between the transmission signal having the uplink frequency ftx and other radio waves (interfering signals), communication between the base station and the mobile terminal 5 becomes impossible. In such cases, the sources of the interfering radio waves have to be tracked down and transmission of the interfering waves have to be stopped. However, it is very difficult to determine the sources of interfering waves, and it is substantially impossible to track down the sources or the directions of the sources utilizing directional antennas especially when the interference waves come from far-off sources, mobile stations, etc.
There have been some techniques proposed for resolving the interference problem. In a conventional mobile radio communication device which is disclosed in Japanese Patent Application Laid-Open No. HEI4-249949, xe2x80x9cCORDLESS TELEPHONExe2x80x9d, a fixed station is provided with a fixed station reception circuit as well as a mobile terminal reception circuit, and the fixed station performs judgment on idle channels by further detecting radio wave signals transmitted by other fixed stations. By the information concerning the idle channels obtained by the detection of the signals from other fixed stations, interference between transmission signals of the fixed station and transmission signals of other fixed stations is avoided.
However, the above second conventional mobile radio communication device needs to be provided with the fixed station reception circuit for detecting transmission signals from other fixed stations and a judgment circuit for performing judgment on idle channels, and thus construction of the mobile radio communication device is necessitated to be complicated.
It is therefore the primary object of the present invention to provide a mobile radio communication device in which the mixing of interfering signals to the downlink frequency and/or the uplink frequency can be avoided and interruption of communication can be prevented, and thereby communication reliability and transmission efficiency can be improved.
Another object of the present invention is to provide a mobile radio communication device in which the avoidance of the mixing of interfering signals can be attained by a simple additional circuit, and thereby enlargement of circuit scale and signal processing scale of the device can be avoided and increase in power consumption can be prevented.
Another object of the present invention is to provide a mobile radio communication device in which the communication carrier frequency can be switched to another frequency when the mixing of interfering signals occurred, and thereby effective use of frequencies can be realized.
Another object of the present invention is to provide a mobile radio communication device in which whether the occurrence of mixing of interfering signals should be informed to the base station or not can be judged and determined on the side of the mobile terminal, and thereby flexibility in usage and device construction of can be increased.
In accordance with a first aspect of the present invention, there is provided a mobile radio communication device for performing communication with a base station comprising an interference detection means and an interference informing means. The interference detection means detects occurrence of the mixing of interfering signals into the downlink frequency and/or the uplink frequency which are used for the communication between the base station and the mobile radio communication device, and the interference informing means transmits information about the occurrence of the mixing of interfering signals into the downlink frequency and/or the uplink frequency to the base station in order to let the base station assign the mobile radio communication device new time slots or a new communication carrier frequency.
In accordance with a second aspect of the present invention, in the first aspect, the mobile radio communication device is provided with a transmission system and two reception systems which are composing a post-detection selective space diversity system in which one demodulated signal is selected from two demodulated signals outputted by the two reception systems based on the levels of RSSI (Received Signal Strength Indicator) signals which correspond to the field intensity of post-detection reception signals, and each of the two reception systems is composed of a double superheterodyne system in which demodulation of the reception signal is executed after two steps of frequency conversions.
In accordance with a third aspect of the present invention, in the first aspect, the communication between the base station and the mobile radio communication device is performed according to TDMA-FDD (Time Division Multiplexing Access-Frequency Division Duplex) method, and transmission by the base station is executed according to TDM (Time Division Multiplexing) method.
In accordance with a fourth aspect of the present invention, in the first aspect, the detection of occurrence of the mixing of interfering signals into the downlink frequency is performed by means of judgment with respect to the data error rate in demodulated reception signals.
In accordance with a fifth aspect of the present invention, in the first aspect, the detection of occurrence of the mixing of interfering signals into the uplink frequency is performed by means of judgment with respect to an RSSI (Received Signal Strength Indicator) signal whose signal level varies corresponding to the field intensity of an interfering reception signal having a carrier frequency equal to the uplink frequency.
In accordance with a sixth aspect of the present invention, in the first aspect, the interference informing means informs the base station of the occurrence of the mixing of interfering signals into the downlink frequency and/or the uplink frequency, using the control channel.
In accordance with a seventh aspect of the present invention, in the first aspect, the interference informing means informs the base station of the occurrence of the mixing of interfering signals into the downlink frequency and/or the uplink frequency, by repeating transmission using the uplink frequency.
In accordance with an eighth aspect of the present invention, in the second aspect, each of the two reception systems includes a reception means provided with an antenna for receiving signals, a first frequency conversion means for converting the reception signal supplied from the reception means into a first intermediate frequency signal, a second frequency conversion means for converting the first intermediate frequency signal supplied from the first frequency conversion means into a second intermediate frequency signal, a demodulation means for demodulating the second intermediate frequency signal supplied from the second frequency conversion means and thereby outputting a demodulated signal, and an RSSI section for outputting an RSSI (Received Signal Strength Indicator) signal whose signal level varies corresponding to the intensity of the second intermediate frequency signal supplied from the second frequency conversion means and thereby indicating the field intensity of the reception signal.
In accordance with a ninth aspect of the present invention, in the eighth aspect, one of the reception systems further includes an antenna function switching means and an interference detection signal generation means. The antenna function switching means switches the function of the antenna of the reception system between reception and transmission by selectively connecting the transmission system to the antenna of the reception system in order to utilize the antenna for transmission. The interference detection signal generation means converts an interfering reception signal having the uplink frequency which has been received by the antenna of the reception system into an interference detection signal whose frequency is equal to the first intermediate frequency, and supplies the interference detection signal to the second frequency conversion means of the reception system so that the mixing of interfering signals into the uplink frequency can be detected.
In accordance with a tenth aspect of the present invention, in the ninth aspect, the interference detection signal generation means includes an antenna common use means, a mixing means, and a selection means. The antenna common use means draws out the interfering reception signal having the uplink frequency which has been received by the antenna of the reception system in the case where the antenna is used for reception of the interfering reception signal, and supplies a transmission signal outputted by the transmission system to the antenna in the case where the antenna is used for transmission. The mixing means mixes the interfering reception signal having the uplink frequency which has been drawn out by the antenna common use means with a reception signal having the downlink frequency which has been received by the antenna of the other reception system and thereby converts the interfering reception signal into the interference detection signal. And the selection means executes selection between the first intermediate frequency signal supplied from the first frequency conversion means and the interference detection signal supplied from the mixing means, and supplies the selected signal to the second frequency conversion means.
In accordance with an eleventh aspect of the present invention, in the tenth aspect, the antenna common use means is a circulator which is placed between the antenna function switching means and the transmission system.
In accordance with a twelfth aspect of the present invention, in the tenth aspect, the interference detection signal generation means further includes a high frequency amplifier which is placed between the antenna common use means and the mixing means.
In accordance with a thirteenth aspect of the present invention, in the eighth aspect, the mobile radio communication device further comprises band pass filters and amplifiers which are placed in front of the first frequency conversion means, between the first frequency conversion means and the second frequency conversion means, and after the second frequency conversion means.
In accordance with a fourteenth aspect of the present invention, in the first aspect, the mobile radio communication device further comprises an automatic information means for automatically activating the interference informing means when occurrence of the mixing of interfering signals into the downlink frequency or the uplink frequency is detected by the interference detection means, and automatically informing the base station of the occurrence of the interference utilizing the interference informing means.
In accordance with a fifteenth aspect of the present invention, in the first aspect, the mobile radio communication device further comprises an interference display means and a manual operation information means. The interference display means displays occurrence of interference when occurrence of the mixing of interfering signals into the downlink frequency or the uplink frequency is detected by the interference detection means. The manual operation information means receives manual operation of the user who has seen the display on the interference display means and who is requesting transmission of information about the occurrence of the interference to the base station, and informs the base station of the occurrence of the interference utilizing the interference informing means if the user executed the manual operation.